Electron bombardment heating apparatus and temperature controlling apparatus and control method thereof

ABSTRACT

An electron bombardment heating apparatus, in which thermions emitted from filaments  9  are accelerated and impinged upon a heating plate  2,  so as to heat the heating plate  2,  wherein a periphery wall of a heated material supporting member  1  having a heating plate as a ceiling thereof is made up with multi-staged periphery wall portions  13   a  and  13   b , being piled up vertically and different in the radius thereof, and those periphery wall portions  13   a  and  13   b  are connected with each other by means of a ring-like horizontal wall  5.  With this, thermal stress can be mitigated, which is caused due to the difference of temperature between the lower end portion of the heated material supporting member  1  and the heating plate  2  when heating up the heating plate  2,  thereby bringing about no breakage in the heated material supporting member if conducting heating and cooling upon the heating plate, repetitively.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a heating apparatus for heatinga material, such as, a semiconductor wafer, etc., to be heated up tohigh temperature, and in particular, an electron bombardment heatingapparatus of a type, in which accelerated electrons are collided orimpinged upon a heating plate, thereby generating heat thereon, and itrelates to such an electron bombardment heating apparatus, inparticular, being superior in thermal stress-resistance, and also atemperature controlling apparatus and a control method of such theelectron bombardment heating apparatus, enabling both; i.e., an increaseof temperature with stability and a maintenance of steady temperature.

[0003] 2. Description of Prior Art

[0004] In processes for treating semiconductor wafers, etc., an electronbombardment heating apparatus of such a type, in which acceleratedelectrons are stroked or impinged upon the rear surface of a heatingplate, thereby generating heat thereon, is widely used as a means forheating up a plate-like material, such as the semiconductor wafer, etc.In such the electron bombardment heating apparatus, thermions generatedthrough conduction of electricity into a filament are accelerated underhigh voltage, to be impinged upon the rear surface of the heating plate,thereby generating heat in the heating plate. And, a plate-like materialmounted on that heating plate is heated up.

[0005]FIG. 6 attached herewith shows such the electron bombardmentheating apparatus, relating to the conventional art. In this FIG. 6,though not shown in the figure, an upper portion of a stage portion 106is located within an inside of a vacuum chamber, and a portion of aheating plate 102 is located within a vacuum atmosphere.

[0006] In a wall of the stage portion 106, there is formed a coolantpassage 107, and through this coolant passage 107 flows a coolanttherein, such as a water, etc., for example, thereby cooling down thestage portion 106.

[0007] On this stage portion 106, there is provided a heat-resistivemember 101 for supporting a material to be heated (hereinafter, beingcalled by a “heated material supporting member”), having the flatheating plate 102 thereon, on which a thin plate-like material, such asa silicon wafer, for example, can be mounted to be heated up, and withinan inside thereof, there is defined a space being hermetically separatedfrom the space of an outside thereof. In more details, the heatedmaterial supporting member 101 is closed by means of the heating plate102 on an upper surface side thereof, while being opened on a lowersurface side, thereby having a cylinder-like shape. A lower end portionof the heated material supporting member 101 is fixed, abutting on anupper surface of the stage portion 106, and it is also hermeticallysealed by means of a vacuum seal member 108.

[0008] As a material for building up such the heated material supportingmember 101 is used, for example, a heat-resistive silicon carbideimpregnated with silicon, or a ceramic, such as, alumina (or aluminumoxide) or silicon nitride, etc. In a case where the heated materialsupporting member 101 is made of an insulating material, such as thesilicon-impregnated silicon carbide, for example, an inner surface ofthe heating plate 102 is metallized for forming a conductive filmthereon, and this conductive film is grounded through the stage portion106.

[0009] On the stage portion 106 is formed an exhaust passage 104, andthe space defined within an inside of the heated material supportingmember 101 is evacuated by means of a vacuum pump 105, which isconnected to that exhaust passage 104, thereby bringing about a vacuumcondition therein.

[0010] Further, within the inside of the heated material supportingmember 101, there is provided filaments 109. Those filaments 109 arelocated behind the heating plate 102 of the heated material supportingmember 101, and further reflectors 103 are provided in the rear side ofthe filaments 109, for the purpose of heat blocking. To those filaments109 mentioned above are connected a filament heating electric powersource 110. Further, between those filaments 109 and the heating plate102 is applied acceleration voltage through the heated materialsupporting member 101 from an electron acceleration electric powersource 111. However, the heating plate 102 is grounded, and therefore itis kept to be a positive potential with respect to those filaments 109.

[0011] In such the electron bombardment heating apparatus as wasmentioned above, the thermions are discharged from those filaments 109,when conducting electricity into the filaments 109 from the filamentheating electric power source 110 while also applying the accelerationvoltage of a certain high voltage between the filaments 109 and theheating plate 102 through the electron acceleration electric powersource 111, and those thermions are accelerated under the accelerationvoltage mentioned above, thereby being impinged upon the lower surfaceof the heating plate 102. For this reason, the heating plate 102 isheated up due to the electron bombardment.

[0012] When the temperature of the heating plate 102 rises up, whilemeasuring the temperature of the heating plate 102 due to theelectromotive force generated in a thermocouple 112 by means of athermometer 114, and when the temperature of the heating plate 102reaches up to a predetermined value, the electric power supplied to thefilaments 109 comes down in an electric power adjustor 117, therebymaintaining the temperature of the heating plate 102 at thepredetermined value. And, when passing a predetermined time period, theelectricity is stopped to be conducted into the filaments 109, therebystopping the heat generation of the heating plate 102, while cooling isstarted by means of the coolant flowing through the coolant passageformed in the stage portion 106, thereby lowering down the temperatureof the heating plate 102.

[0013] The heated material supporting member 101 is cooled down on thelower end surface thereof, through the coolant, such as the water, etc.,flowing through the coolant passage 107 of the stage portion 106; e.g.,via the stage portion 106. On the other hand, the heating plate 102building up an upper wall of the heated material supporting member 101is heated up, through the bombardment of the electrons, which aredischarged from the filaments 109 and accelerated by means of theelectron acceleration electric power source 111 of high voltage. Forthis reason, a steep thermal gradient is established, in particular,between the heating plate 102 for building up the upper wall of theheated material supporting member 101 and the lower end portion of theheated material supporting member 101 in contact with the stage portion106.

[0014] However, the heated material supporting member 101 is made of,for example, the heat-resistive silicon carbide impregnated withsilicon, or the ceramic, such as, alumina (or aluminum oxide), orsilicon nitride, etc., therefore it is weak in the thermal stress. Forthis reason, when starting the heating of the heating plate 102, onlythe heating plate 102 for building up the upper wall of the heatedmaterial supporting member 101 shows the thermal expansion. Accompanyingthis, the heated material supporting member 101 deforms, and the thermalstress is concentrated, in particular, upon a shoulder portion definedbetween a peripheral wall portion and the heating plate 102. And, ifrepeating such the heating and the cooling on the heating plate 102, theheated material supporting member 101 receives the thermal stress,repetitively, and therefore there is brought about a problem that it isfatigued and deteriorated, gradually, thereby resulting into breakagethereof.

BRIEF SUMMARY OF THE INVENTION

[0015] According to the present invention, by taking such the problemsmentioned above in relation to the conventional electron bombardmentheating apparatus into the consideration, an object is to provide anelectron bombardment heating apparatus, with which the thermal stresscan be relieved or mitigated, being generated due to the difference intemperature between the heating plate, which is heated through theelectron bombardment of the heated material supporting member thereon,and the lower end portion of the heated material supporting member,which is cooled down through the stage portion. With this, the heatedmaterial supporting member is hardly fatigued even if repeating theheating and the cooling on the heating plate, thereby causing nobreakage therein for a long time period.

[0016] According to the present invention, for accomplishing the objectmentioned above, a heated material supporting member having a heatingplate as a ceiling thereof is formed into, not a cylindrical shapehaving a single radius, but that having at least one (1) stage or morein a middle portion thereof. Namely, upper and lower portions of theheated material supporting member are made up with multi-stagedperiphery wall portions in a cylinder-like shape, being different in theradius thereof, and those periphery portions are connected with by meansof a ring-like horizontal wall extending into the radial directionsthereof. With this, thermal stress caused due to the difference oftemperature between the heating plate of the heated material supportingmember and the lower end portion thereof can be mitigated, by means ofthe multi-staged periphery wall portions and the horizontal wallconnected therewith, thereby protecting it from breaking in an earlystage thereof.

[0017] Thus, according to the present invention, there is provided anelectron bombardment heating apparatus, for heating a heating platethrough bombardment of thermions thereon, comprising: a filament forgenerating thermions therefrom; means for accelerating the thermionsemitted from said filament; a heating plate being heated throughbombardment of the thermions, which are emitted and accelerated; and aheated material supporting member for mounting a material to be heatedthereon, wherein a periphery wall of said heated material supportingmember, being covered with said heating plate on a ceiling thereof, ismade up with a plural number of stages of periphery wall portionsdisposed vertically, being different from each other in diameterthereof, and those periphery wall portions are connected with each otherthrough a ring-like horizontal wall extending in radial directionsthereof.

[0018] With such the electron bombardment heating apparatus, accordingto the present invention, since the periphery wall of the heatedmaterial supporting member including the heating plate as a ceilingthereof is made up with the multi-staged periphery wall portions, beingdifferent in the radius, in the vertical direction thereof, and sincethose periphery wall portions are connected with each other through thering-like horizontal wall extending into the radial directions thereof,the thermal stress can be mitigated, by means of the multi-stagedperiphery wall portions and the horizontal wall connecting therewith, ifthe difference is caused in the temperature between the heating plate ofthe heated material supporting member and the lower end portion thereof,when heating. In particular, since the shoulder portion formed on theheated material supporting member, where the thermal stress canconcentrate thereupon, easily, comes to be more than (1) pieces,therefore it is difficult for the thermal stress concentrates on aspecific shoulder portion. Accordingly, it is possible to bring thethermal stress to be small, which is applied upon the heated materialsupporting member as a whole, and even if repeating the heating and thecooling down to the room or steady temperature, it can be protected frombreaking in the early stage thereof.

[0019] Further, according to the present invention, an insulator platehaving high insulating property and heat-resistance, such as, a ceramicplate, etc., is inserted between the plural numbers of the metalreflectors. The reflector 3 below the insulator plate 20 is one, beingprovided for the purpose of heat insulation but without electricalconnection, and the reflector(s) above the insulator plate 20 is/areone(s), having functions of both, i.e., preventing electrons fromdischarging to a rear side thereof, and the heat insulation.

[0020] Further, according to the present invention, in such the electronbombardment heating apparatus as was mentioned in the above, the thermalcontrol when rising up the temperature and the thermal control whenmaintaining at the steady temperature are carried out by means ofcontrol methods separated from. In more details, when rising up thetemperature, a total amount of energy of electrons impinging upon theheating plate is controlled to be a constant through controlling theelectric power to be supplied to the filament while measuring theemission current, thereby maintaining the thermal gradient at the presetvalue. In addition thereof, the temperature of the heating plate ismeasured, and after the heating plate reaches up to the predeterminedtemperature, the electric power for conducting electricity to thefilament by means of the measured value of temperature, therebymaintaining the heating plate at the predetermined value that is set inadvance.

[0021] A temperature controlling apparatus, according to the presentinvention, for achieving such the thermal control as was mentionedabove, comprising: an electric power adjuster for controlling filamentelectric power to be supplied to the filament; an emission currentadjuster, for measuring emission current flowing between the filamentand the heating plate, and for outputting a measurement value of theemission current to said electric power adjuster as a control signal;and a thermal adjuster for measuring the temperature of the heatingplate and for outputting the measured temperature value to said electricpower adjuster as a control signal, wherein either one of said emissioncurrent adjuster or said thermal adjuster is selectively exchanged to beconnected with the electric power adjuster, by means a switch.

[0022] A method for controlling temperature of the heating plate, bymeans of such the temperature controlling apparatus, including thereinan electric power adjuster for controlling filament electric power to besupplied to the filament, comprising the following steps of: controllingemission current to be a preset value by means of said electric poweradjuster, while measuring the emission current flowing between thefilament and the heating plate by means of an emission current adjuster,when the temperature of the heating plate rises up; and also controllingthe temperature of the heating plate to be a preset temperature by meansof said electric power adjuster, while measuring the temperature of theheating plate by means of a thermal adjuster, after the measuredtemperature reaches to a preset temperature. In this instance, a switchis changed over upon a fact that the measured value of temperaturemeasured by said thermal adjuster reaches to the preset temperature ortemperature a little bit lower than the preset temperature.

[0023] With such the temperature controlling apparatus and the methodfor the electron bombardment heating apparatus, the emission currentflowing between the filament and the heating plate is set in advance,and then when temperature of the heating plate rises up, said electricpower adjuster is controlled by means of the emission current adjusterso that the emission current comes to be constant while measuring thisemission current. With this, it is possible to give a constant electronbombardment upon the heating plate per an hour, thereby obtaining aconstant thermal gradient with stability.

[0024] At the same time, measuring the temperature of the heating plateby means of the thermal adjuster, the electric power adjuster isswitched to the side of the thermal adjuster when temperature of theheating plate reaches to the predetermined one, thereby conducting thethermal control with feeding the temperature of the heating plate backto the electric power adjuster. With this, it is possible to maintainthe predetermined temperature to be steady in condition, with accuracyand stability.

[0025] In this manner, with the electron bombardment heating apparatusaccording to the present invention, since the thermal stressaccompanying thermal change is dispersed due to the plural numbers ofstages of the heated material supporting member and the horizontal wall,the fatigue breaking hardly occurs thereon in spite of the thermalstress, which is caused by repeating the heating and the coolingrepetitively. For this reason, it is possible to protect the heatedmaterial supporting member from being destroyed in the early stage, andthereby to obtain the heated material supporting member having a longerlifetime.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0026] Those and other objects, features and advantages of the presentinvention will become more readily apparent from the following detaileddescription when taken in conjunction with the accompanying drawingswherein:

[0027]FIG. 1 is a vertical cross-section view of an outlook structure ofan electron bombardment heating apparatus, for showing an embodimentaccording to the present invention;

[0028]FIG. 2 is a cross-section view of a principle portion of theelectron bombardment heating apparatus, in particular, for showing aportion of a heated material supporting member thereon, in theembodiment mentioned above;

[0029]FIG. 3 is a graph attaching a chart therein, for showing anexample of the relationship between time and temperature when heating upthe heating plate, and also the chart of temperature control at thatinstance therein;

[0030]FIG. 4 is a vertical cross-section view of an outlook structure ofan electron bombardment heating apparatus, for showing other embodimentaccording to the present invention;

[0031]FIG. 5 is a vertical cross-section view of an outlook structure ofan electron bombardment heating apparatus, for showing further otherembodiment according to the present invention, in which the structure ofa reflector portion is changed; and

[0032]FIG. 6 is a vertical cross-section view of an outlook structure ofthe electronic bombardment heating apparatus, relating to theconventional art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Hereinafter, embodiments according to the present invention willbe fully explained, by referring to the drawings attached herewith.

[0034]FIG. 1 is a cross-section view of an outlook structure of theelectron bombardment heating apparatus, for showing an embodimentaccording to the present invention, wherein an upper portion of a stageportion 6 is located within an inside of a vacuum chamber, and a portionof a heating plate 2 is within the vacuum atmosphere, in the similarmatter of the conventional art, as was mentioned in the above byreferring to FIG. 6.

[0035] In a wall of the stage portion 6 is formed a coolant passage 7,and the stage portion 6 is cooled down through a coolant, such as awater, etc., flowing through that coolant passage 7.

[0036] On this stage portion 6 is provided a heat-resistive member 1 forsupporting a material to be heated (hereinafter, being called by “heatedmaterial supporting member”), having the flat heating plate 2 thereon,on which a thin plate-like material, such as a silicon wafer, etc., canbe mounted to be heated up, and within an inside thereof, there isdefined a space being hermetically separated from the space of anoutside thereof. In more details, the heated material supporting member1 is closed by means of the heating plate 2 on an upper surface sidethereof, while being opened on a lower surface side thereof, therebyhaving a cylindrical shape, and a flat upper surface of the heatingplate 2 is wider than the thin plate-like material to be heated up, suchas, the silicon wafer, etc. A flange is provided at the lower endportion of the heated material supporting member 1, and this flangeportion is fixed on an upper surface of the stage portion 6 abuttingthereon, and it is hermetically sealed by means of a vacuum seal member8.

[0037] The heated martial supporting member 1 is made of silicon carbideimpregnated with silicon, or a ceramic, such as, alumina (or aluminumoxide) or silicon nitride, etc. In a case where the heated materialsupporting member 1 made of an insulating material, such as,silicon-impregnated silicon carbide, for example, an inner surface ofthe heating plate 2 is metallized for forming a conductive film thereon,and this conductive film is grounded through the stage portion 6. Also,the same object can be achieved, by including conductive materialswithin the material for building up the heating plate 2, so as to let itto show conductivity.

[0038] As is shown in FIG. 1, a periphery wall of the heated materialsupporting member 1 is large, in the diameter at a lower stage thereof,while being small in the radius at an upper stage thereof, therefore, ithas a cylindrical shape of two (2) stages. The periphery wall portion13b being large in the radius at the lower stage and the periphery wallportion 13a being small in the radius at the upper stage are connectedwith, by means of a ring-like horizontal wall 5, extending into a radialdirection of that periphery wall. Those periphery wall portions 13a and13b, being different in the radius thereof, and also the horizontal wall5 connecting them may be formed, preferably, in one body or as one unit.

[0039] In the stage portion 6 is formed an exhaust passage 4, and thespace defined within an inside of the heated material supporting member1 is evacuated by means of a vacuum pump 5, which is connected to thatexhaust passage, thereby bringing about the vacuum condition therein.

[0040] Further, within an inside of the heated material supportingmember 1, there are provided filaments 9 and reflectors 3.

[0041] The filaments 9 are provided in the rear side of the heatingplate 2 of the heated material supporting member 1, and to thosefilaments 9 is connected a filament heating electric power source 10through an insulator seal terminal. This filament heating electric powersource 10 is insulated, so that voltage is high at a side of thefilaments 9 while it is low at a side of a voltage adjuster 17.Furthermore, between the filaments 9 and the heating plate 2 is appliedvoltage for acceleration through the heated material supporting member1, by means of an electron acceleration electric power source 11.However, the heating plate 2 is grounded, and it is kept at a positivepotential with respect to the filaments 9.

[0042] The reflectors 3 are provided in the rear side of the filaments9, with respect to the heating plate 2 of the heated material supportingmember 1. This reflector is made of a metal having high reflectivity,such as gold (Au), silver (Ag), etc., or a metal having high meltingpoint, such as, molybdenum, etc. A surface of the reflector 3, opposingto the heating plate 2 of the heated material supporting member 1, ismade from a mirror surface, thereby reflecting the radiant heatthereupon. Though being electrically insulated from the heated materialsupporting member 1, however those reflectors 3 are positioned under thepotential condition of being about equal to that of the filaments 9.With this, no electron comes flying toward the reflectors 3, therebycausing no heating due to the electron bombardment thereupon. Such thefilaments 9 can be disposed in duplicate.

[0043] In the central portion of the reflector 3, a shield 15 made froma cylinder-like conductor stands up, and this shield 15 and thereflectors 3 are electrically conducted with each other; i.e., beingequal in the potential thereof. An upper end side of this shield 15reaches up to the vicinity of the lower surface of the heating plate 2of the heated material supporting member 1, while a flange is providedextending from the upper end portion of that shield 15 to an outside,and therefore this flange faces to the lower surface of the heatingplate 2.

[0044] A sheath-type thermocouple 12 is inserted into vertically, fromthe central portion of the stage portion 6 mentioned above, as atemperature measuring element, and an upper end side of this is disposedwithin the shield 15 under the non-contacting condition thereon. Theupper end of this thermocouple 12, connecting a pair of lines ofthermocouple as a junction, builds up a temperature measurement pointwithin the shield 15 mentioned above, and the temperature measurementpoint is in contact with the lower surface of the heating plate 2 via aninsulator tube. The thermocouple 12 is wired out from the stage portion6 into an outside of the vacuum chamber, and a compensation lead wire isconnected to a thermometer 14 including a zero point compensationcircuit therein.

[0045] With such the electron bombardment heating apparatus, thethermions are emitted from the filaments 9 when conducting electricityto the filaments 9 by means of the filament heating electric powersource 10, while applying a certain high voltage for accelerationbetween the filaments 9 and the heating plate 2, by means of theelectron acceleration electric power source 11, and those emittedthermions are accelerated under the acceleration voltage mentionedabove, and impinge upon the lower surface of the heating plate 2. Forthis reason, the heating plate 2 is heated up due to the electronbombardment thereupon. In this instance, the coolant flows through thecoolant passage 7 formed in the stage portion 6, and thereby the heatedmaterial supporting member 1 is cooled down.

[0046] The temperature of the heating plate 2 rises up, while measuringthe temperature of the heating plate 2 by means of the thermocouple 12,and when the temperature of the heating plate 2 reaches up to apredetermined value, then the filament heating electric power source 10for conducting electricity to the filaments 9 is lowered down in theelectric power thereof, and then the heating plate 2 is maintained at apredetermined temperature. When passing a predetermined time period, theelectricity is stopped to be conducted into the filaments 9, thereby tostop the heat generation of the heating plate 2, while the cooling isstared by means of the coolant flowing through the coolant passageformed in the stage portion 6, thereby lowering down the temperature ofthe heating plate 2.

[0047] In this manner, the lower end portion of the heated materialsupporting member 1 is cooled down by means of the cooling water flowingthrough the coolant passage 7 formed in the wall of the stage portion 6,when heating up the heating plate 2. For this reason, a large thermalgradient is established between the lower end portion of the heatedmaterial supporting member 1 and the heating plate 2. On the other hand,before the time when heating up the heating plate 2 and during the timewhen cooling it, both the lower end portion of the heated materialsupporting member 1 and the heating plate 2 are in the vicinity of theroom or steady temperature, therefore there is established no thermalgradient therebetween. In this manner, with repetition of heating andcooling, a large change is caused on the thermal gradient establishedbetween the lower end portion of the heated material supporting member 1and the heating plate 2, repetitively.

[0048] In this instance, as is shown in FIG. 2, though the heating plate2 of the heated material supporting member 1, the upper and lowerperiphery wall portions 13a and 13b, and the horizontal wall 5 expand,and thereby deforming, respectively, however the expansion mentionedabove can be absorbed by the walls neighboring with each other. Further,comparing to the conventional electron bombardment heating apparatusshown in FIG. 6 mentioned above, wherein the only one (1) piece ofshoulder portion is defined between the heating plate 2 of the heatedmaterial supporting member 1 and the periphery wall portions, howeveraccording to the electron bombardment heating apparatus shown in FIG. 1,the shoulder portions are defined by three (3) in the pieces thereof,and therefore the stress concentrating upon the shoulder portions can bedispersed much more between them. With this, even if applying theheating and the cooling thereon, repetitively, it is difficult to causethe breakage, in an early stage thereof, due to the thermal stressapplied thereon repetitively.

[0049] Next, the structure of a temperature controller for use of suchthe electron bombardment heating apparatus will be explained, byreferring a block diagram, which is inserted into FIG. 1 mentionedabove.

[0050] There is provided an electric power adjuster 16 for the purposeof adjusting current and voltage for heat generation to be supplied tothe filaments 9, in other words, electric power of the filament heatingelectric power source 10 for supplying current for use of emission ofthermions to the filaments 9.

[0051] Further, there are provided an emission current adjuster 17 forthe purpose of outputting a control signal to the electric poweradjuster 16, and also a thermal regulator 18.

[0052] The emission current adjuster 17 has a function of setting ordetermining the emission current flowing between the heating plate 2side and the filaments 9 at a predetermined value. Furthermore, whilemeasuring the emission current, this emission current adjuster 17outputs a control signal to the electric power adjuster 16, so that theemission current is maintained at a predetermined preset value, therebyadjusting the current and the voltage of the filament heating electricpower source 10 for conducting electricity to the filaments 9, by meansof this electric power adjuster 16.

[0053] On the other hand, the thermal regulator 18 has functions ofsetting the steady temperature of the heating plate 2 at a predeterminedtemperature, and also of setting a time period for maintaining thatsteady temperature. Further, while measuring the temperature on thelower surface of the heating plate 2 by means of the thermocouple 12 andthe thermometer 14 connected thereto, this thermal regulator 18 outputsa control signal to the electric power adjuster 16, so that thetemperature of the heating plate 2 is maintained at the predeterminedpreset value mentioned above, thereby adjusting the current and thevoltage of the filament heating electric power source 10 for conductingelectricity to the filaments 9, by means of this electric power adjuster16.

[0054] Also, the thermal regulator 18 actuates a switch 19 of a relay,etc., for example. During when the temperature rises up, but before thetemperature measured in the thermometer 14 by means of the thermocouple12 reaches up to the steady temperature, which is reset by means of thethermal regulator 18, the emission current adjuster 17 is connected tothe electric power adjuster 16. Thereafter, when the temperaturemeasured in the thermometer 14 reaches up to the steady temperaturepreset by means of the thermal regulator 18, the switch 19 is changedover, so that the thermal regulator 18 is connected to the electricpower adjuster 16.

[0055] Next, explanation will be given on a method for controlling thetemperature of the electron bombardment heating apparatus, with aid ofthis temperature controller.

[0056] First of all, the emission current to be maintained at constantwhen temperature rises up is set up in advance, by means of the emissioncurrent adjuster 17, depending upon the thermal gradient when thetemperature of the heating plate 2 rises up.

[0057] Also, by means of the thermal regulator 18, temperature to bemaintained at constant is set up in advance, depending upon an object ofthermal treatment or processing of the material to be heated up.

[0058] When starting conduction of electricity into the filaments 9through the filament heating electric power source 10, while applyingthe constant high voltage for acceleration between the filaments 9 andthe heating plate 2, at the same time, by means of the electronacceleration electric power source 11, then the thermions are emittedfrom the filaments 9, and those thermions, being accelerated under theacceleration voltage mentioned above, impinge upon the lower surface ofthe heating plate 2. For this reason, the heating plate 2 is heated updue to the electron bombardment. At the same time, emission currentflows through between the filaments 9 and the heating plate 2. In thisinstance, the acceleration voltage applied through the electronacceleration electric power source 11 is made constant.

[0059] During when the temperature of the heating plate 2 rises up, butbefore it reaches up to the steady temperature, which is set up inadvance by means of the thermal regulator 18 mentioned above, theemission current adjuster 17 is connected to the electric power adjuster16. This emission current adjuster 17, while measuring the emissioncurrent flowing between the heating plate 2 side and the filaments,outputs a control signal to the electric power adjuster 16, so that theemission current is maintained at the preset value thereof, therebyadjusting the voltage and the current of the filament heating electricpower source 10 for conducting electricity to the filaments 9, by meansof this electric power adjuster 16. With this, the emission currentflowing between the heating plate 2 side and the filaments 9 ismaintained at the constant value when the hating plate 2 rises up thetemperature thereof. As was mentioned previously, the accelerationvoltage, which is applied by means of the electron acceleration electricpower source 11, is constant, and also the emission current ismaintained at the constant value. For this reason, the energy, given tothe heating plate 2 due to the electron bombardment, comes to beconstant, and the heating plate 2 rises up the temperature thereof, at aconstant thermal gradient.

[0060] Thereafter, when the temperature of the heating plate 2 reachesup to the steady temperature, which is preset by means of the thermalregulator 18 mentioned above, the switch is actuated, so as to changeover the contact thereof, and therefore, the thermal regulator 18 isconnected to the electric power adjuster 16. This thermal regulator 18,obtaining or receiving the signal from the thermometer 14 for measuringthe temperature on the lower surface of the heating plate 2 by means ofthe thermocouple 12, outputs a control signal to the electric poweradjuster 16, so that the temperature of the heating plate 2 ismaintained at the steady temperature, which was preset in the mannermentioned above, thereby adjusting the current and the voltage of the ofthe filament heating electric power source 10 for conducting electricityto the filaments 9, by means of this electric power adjuster 16. Withthis, the temperature of the heating plate 2 is maintained at the steadytemperature preset. And, when passing the time period that is preset inthe thermometer 14, the electricity is stopped to be conducted from theelectron acceleration electric power source 11 to between the filaments9 and the heating plate 2, thereby lowering down the temperature of theheating plate 2.

[0061]FIG. 3 shows an example of a relationship between the time and thetemperature when heating up the heating plate 2, and also a chart forcontrolling the temperature in this instance.

[0062] As is shown in the figure, when the temperature rises up, i.e.,from the time of starting the heat generation of the heating plate 2 upto the time of reaching to the steady temperature preset, the electricpower of the filament heating electric power source 10 is controlled, sothat the preset emission current comes to be constant, while measuringthe emission current, so as to feed it back to the electric poweradjuster 16. Since the energy given to the heating plate 2 due to theelectron bombardment is determined by the product between the emissioncurrent and the acceleration voltage, therefore, with this control, dueto the electron bombardment, a constant amount of energy is given to theheating plate 2 per an hour, when rising up the temperature of theheating plate 2.

[0063] On the other hand, after the heating plate 2 reaches up to thepreset steady temperature, the electric power of the filament heatingelectric power source 10 is controlled, so that the preset steadytemperature comes to be constant, while measuring the temperature of theheating plate 2, so as to feed it back to the electric power adjuster16. With this, for a time period preset, the heating plate 2 maintainsthe preset constant temperature, steadily.

[0064]FIG. 4 shows other embodiment of the electron bombardment heatingapparatus, according to the present invention, wherein the elements,similar to those in the embodiment of the electron bombardment heatingapparatus that was shown in FIG. 1 mentioned above, are also given withthe same reference numerals thereto. The embodiment of the electronbombardment heating apparatus shown in this FIG. 4 is almost similar tothe embodiment of the electron bombardment heating apparatus shown inFIG. 1 mentioned above, and therefore, explanation will be given onlyabout the portions differing from that. Thus, in the embodiment shown inFIG. 4, the periphery wall portion 13a having a small radius is locateddown while the periphery wall portion 13b having a large radius up, andthey are also connected with each other, by means of the horizontal wallprovided therebetween. Comparing to the embodiment shown in FIG. 1mentioned above, it is possible to achieve the heating panel 2, beingwider in an area thereof, as the ceiling of the heated martialsupporting member 1.

[0065]FIG. 5 shows further other embodiment of the electron bombardmentheating apparatus, according to the present invention, wherein theelements, similar to those in the embodiment of the electron bombardmentheating apparatus that was shown in FIG. 1 mentioned above, are alsogive with the same reference numerals thereof.

[0066] The higher the temperature of the heating plate 2, the more thethermal loss due to the radiant heat, even if trying to heat up theheating plate 2 through the electrons. Then, it is necessary to increasethe number of pieces of the reflectors for reflecting the radiant heatthereupon. In general, for every increase of temperature of one hundredcentigrade (100° C.) of the heating plate 2, it is necessary to increasethe number of pieces of the reflectors 3 by one (1) piece. However, withsuch the reflectors 3 as shown in FIG. 1 mentioned above, each beingmade from a metal plate, wiring is needed between them, so as to bringthe filaments 9 and the reflectors 3 to be equal in the potentialthereof, for the purpose of preventing electricity from dischargingtowards the heating plate 2 and the opposite side thereof.

[0067] Then, for necessitating no such the wiring, as shown in FIG. 5,between a plural numbers of metal reflectors 3 is inserted an insulatorplate 20, such as, a ceramic plate, etc., for example, having highinsulation and high heat-resistance, thereby insulating the reflectors 3piled up vertically, from each other. The reflector 3 below theinsulator plate 20 is one, being provided for the purpose of heatinsulation, but without electrical connection, while the reflectors 3above the insulator plate 20 are ones, each having functions of both;i.e., preventing electrons from being discharged to a rear side thereof,and for the heat insulation.

[0068] However, in the three (3) embodiments mentioned in the above, theperiphery wall of the heated material supporting member 1 is dividedinto the two (2) stages of the periphery wall portions, being differentin the radium thereof, but in particular, by taking easiness or the likein production thereof into the consideration, but it is also possible todivide the periphery wall of the heated material supporting member 1into three (3) or more stages of the periphery wall portions, beingdifferent in the radium thereof. Though an increase of the number ofstages of the periphery wall portions brings about an improvement on theproperty of dispersing the thermal stress thereupon, however on theother hand, it increases fragility thereof with respect to otherexternal force, and therefore, it is the best to divide the peripherywall into two (2) stages, and it may limited up to three (3) stages atthe largest.

[0069] The present invention may be embodied in other specific formswithout departing from the spirit or essential feature orcharacteristics thereof. The present embodiment(s) is/are therefore tobe considered in all respects as illustrative and not restrictive, thescope of the invention being indicated by the appended claims ratherthan by the forgoing description and range of equivalency of the claimsare therefore to be embraces therein.

What is claimed is:
 1. An electron bombardment heating apparatus, forheating a heating plate through bombardment of thermions thereon,comprising: a filament for emitting thermions therefrom; means foraccelerating the thermions emitted from said filament; a heating platebeing heated through bombardment of the thermions, which are emitted andaccelerated; and a heated material supporting member for mounting amaterial to be heated thereon, wherein a periphery wall of said heatedmaterial supporting member, being covered with said heating plate on aceiling thereof, is made up with a plural number of stages of peripherywall portions disposed vertically, being different from each other indiameter thereof, and those periphery wall portions are connected witheach other through a ring-like horizontal wall extending in radialdirections thereof.
 2. The electron bombardment heating apparatus, asdescribed in the claim 1, wherein said heated material supporting memberis made of ceramic.
 3. The electron bombardment heating apparatus, asdescribed in the claim 2, wherein said heated material supporting memberis made of silicon carbide impregnated with silicon.
 4. The electronbombardment heating apparatus, as described in the claim 1, wherein aheat-resistive insulator plate is inserted between the plural pieces ofsaid reflectors.
 5. A temperature controlling apparatus for an electronbombardment heating apparatus, for controlling temperature due to heatgeneration of a heating plate in the electron bombardment heatingapparatus, in which the heating plate is heated through impingement ofaccelerated thermions emitted from a filament thereupon, comprising: anelectric power adjuster for controlling filament electric power to besupplied to the filament; an emission current adjuster, for measuringemission current flowing between the filament and the heating plate, andfor outputting a measurement value of the emission current to saidelectric power adjuster as a control signal; and a thermal adjuster formeasuring the temperature of the heating plate and for outputting themeasured temperature value to said electric power adjuster as a controlsignal, wherein either one of said emission current adjuster or saidthermal adjuster is selectively exchanged to be connected with theelectric power adjuster, by means a switch.
 6. The temperaturecontrolling apparatus for an electron bombardment heating apparatus, asdescribed in the claim 5, wherein the switch is changed over upon a factthat the measured temperature value, which is measured by means of saidthermal adjuster, reached to a preset temperature that is set inadvance.
 7. A method for controlling temperature due to heat generationof a heating plate for use in an electron bombardment type heatingapparatus, in which the heating plate is heated through impingement ofaccelerated thermions emitted from a filament thereupon, includingtherein an electric power adjuster for controlling filament electricpower to be supplied to the filament, comprising the following steps of:controlling emission current to be a preset value by means of saidelectric power adjuster, while measuring the emission current flowingbetween the filament and the heating plate by means of an emissioncurrent adjuster, when the temperature of the heating plate rises up;and controlling the temperature of the heating plate to be a presettemperature by means of said electric power adjuster, while measuringthe temperature of the heating plate by means of a thermal adjuster,after the temperature reaches to a preset control temperature ortemperature a little bit lower than the preset temperature.
 8. Themethod for controlling temperature for an electron bombardment typeheating apparatus, as described in the claim 7, wherein exchange betweenthe emission current adjuster and the thermal adjuster is conducted bymeans of a switch, when the measured value of the temperature of theheating plate by means of the thermal adjuster reaches to a presettemperature which is set in advance.